Display case



United States Patent ()fiice 3,365,908 Patented Jan. 30, 1968 3,365,908 DISYLAY CASE Malcolm ll). li/iacMaster, Yardley, Pa, assignor to Ernhart Corporation, Bioomfield, Comm, a corporation of Connecticut Filed Sept. 15, 1966, S01. No. 579,693 12 Claims. ((31. 62-256) This invention relates to refrigerated display cases and is directed particularly to display cases having an access opening in the front thereof with means for establishing an air curtain consisting of multiple layers of air directed across the access opening to minimize the entry of warm moist ambient air into the display space.

Refrigerated display cases having an access opening in the front thereof and an air curtain flowing across the opening are widely used in the display and storage of a great variety of food products. Some products, such as dairy products, eggs, meats and the like are ordinarily refrigerated to a limited extent-that is to temperatures above freezingsay about 40 F., whereas other products such as frozen foods, ice cream and the like must be maintained at all times below 32 F. and preferably at temperatures of F. or below.

The temperature of the air circulated about the display space and forming the air curtain therefor will differgreatly depending upon the intended use of the case and the nature of the products to be stored and displayed therein. However, in all display cases of this character, the temperature of the display space and at least the inner layer of air circulated in forming the air curtain are reduced below the temperature of the ambient air. Refrigerating means of suitable capacity are therefore provided for reducing the temperature of the display space and the air curtain to suitable low temperatures. For this purpose, one or more evaporators are located within one or more passages through which air is circulated by a lower and passed in heat exchanging relation with the display space and across the access opening.

The air thus circulated tends to pick up moisture due in part to the entrainment of ambient air as it flows across the access opening and in part due to the penetration of ambient air through the air curtain as persons reach into the case to inspect or remove articles from the display space. As a result, the evaporators employed for refrigcrating the circulated air become coated with frost, ice or snow and must be defrosted from time to time by heating the evaporators or raising the temperature of the air passed over same. The refrigerating cycle used normally includes a relatively long period of refrigeration and a relatively short defrost period during which the refrigerating means is rendered inactive and the evaporators are heated by means of electrical heating elements or otherwise. However, the blowers generally are operated during the defrosting cycle in order to reduce the penetration of warm, moist, ambient air into the display space.

When such self service display cases are used for dairy products and the like, and are operated at temperatures above freezing, there is a tendency for moisture introduced through the air curtain by customers or evaporating from tie packages or articles introduced for display, to condense on the refrigerated rear walls, shelves, and other surfaces exposed to the interior of the display space. When this occurs, the case is said to sweat and the articles are rendered damp and packages may become sodden or damaged.

On the other hand, when such display cases are operated at temperatures below freezing, the surfaces ex posed to the interior of the display space undergo a considerable rise in temperature during the defrosting cycle of operation when air at temperatures above freezing is circulated in heat exchanging relation therewith to remove ice and frost therefrom and from the coils and tins of the evaporators employed for refrigerating the case. At such times, there is a tendency for those packages or articles in contact with the rear walls or shelves in the display space, or adjacent thereto to melt or become moist as a result of the rise in temperature. Thereafter, when the refrigerating operation is renewed, the packages become frozen to each other or to the rear walls or shelves so as to render it difiicult to remove the same from the case. Moreover, such melting and refreezing of articles such as ice cream or frozen vegetables causes the products to deteriorate or become unfit for sale.

In accordance with the present invention, a novel type of self service refrigerated display case is provided which is adapted for use in the display and marketing of products at temperatures either above freezing or below freezing depending essentially upon the capacity and type of the refrigerating elements employed. At the same time, the display case is so constructed that objectionable sweating thereof when operated at temperatures above freezing will not occur, whereas melting and refreezing of articles as a result of alternate defrosting and refrigcrating cycles of operation will not take place when the case is normally maintained at temperatures below freezing.

These results are preferably attained by limiting the rate of heat transfer through the walls or surfaces exposed to the interior of the display space while circulating refrigerated air about said space and in the form of an air curtain across the access opening to said space.

Accordingly, the principal objects of the present invention are to extend the utility of self service refrigerated display cases; to reduce the tendency for surfaces exposed within the display space of such cases to sweat or to become wet during either refrigeration or defrosting cycles of operation or refrigerating means employed therewith; and to improve the operation of self service refrigerated display cases having an access opening in the front thereof across which an air curtain is directed.

A specific object of the present invention is to provide self service refrigerated display cases wherein air is circulated about a display space and across an access opening, with means for limiting the rate of heat transfer through surfaces exposed to the interior of the display space.

These and other objects and features of the present invention will appear from the following description thereof wherein reference is made to the figures of the accompanying drawings.

In the drawings:

FIG. 1 is a vertical sectional view through a typical form of self service display case for food products embodying the present invention;

FIG. 2 is a horizontal sectional view through a portion of the construction illustrated in FIG. 1 taken on the line 2-2 of FIG. 1;

FIG. 3 is a front elevation of the portion of the rear surface of the display case illustrated in FIG. 2; and

FIG. 4 is a vertical sectional view through an alternative type of display case embodying the present invention.

In that form of the invention chosen for purposes of illustration in FIGS. 1, 2 and 3 of the drawings, the display case has an insulated base 2, an insulated rear wall t, an insulated top'6 and a lower insulated front Wall 8 which is spaced from the top of the case to provide a forwardly facing access opening 10. Refrigerating means in the form of an evaporator 12 are located adjacent the bottom of the case and if desired a second evaporator 14 may also be used to serve as a dehydrating and supplemental refrigerating means.

3 The display space 16 within which the products to be stored and displayed are located is defined by a bottom panel 18 positioned above the evaporator or evaporators 12 and 14, and by a vertical rear panel 26 which is spaced from the insulated rear Wall 4 of the case a suihcient distance to provide for a vertically extending inner refrigerated air duct 22 and a parallel vertically extending outer protective air duct 24. The top of the display space is defined by a panel 26 which extends forward from the upper end of the rear panel 20 of the display space and is spaced from the insulated top 6 a distance sufficient to provide for the forwardly extending portion 28 of the inner refrigerated air duct 22 and the forwardly extending portion 30 of the outer protective air duct 24.

The forward end of the forwardly extending portion 3% of the outer protective air duct 24 terminates in a downwardly directed outlet opening 32 through which an outer protective layer of air 34 is caused to flow across the access opening of the display case to the inlet 36 of an outer return air passage 38 located adjacent the inner side of the lower insulated front wall 8 of the display case. In a similar way, the forward end of the forwardly extending portion 28 of the inner refrigerated air duct 22 terminates in a downwardly directed outlet opening 44 which may be directly adjacent the outlet opening 32, and serves to cause an inner refrigerated layer of air 42 to flow across the access opening 10 to inner refrigerated air inlet 44 of an inner cold air return passage 46.

The protective layer of air 34 and the refrigerated layer of air 42 cooperate to form an air curtain 48 which may include one or more additional layers of air if desired and serves to prevent or diminish the passage of warm, moist, ambient air into the display space while permitting customers standing in front of the display case to reach into the display space to remove articles 50 from the well 52 above the bottom panel 18 of the display space and articles 54 from the shelves 56, 58, 60 etc. which project forwardly from the rear panel of the display space.

In order to establish and maintain the air curtain 48, a blower 62 is arranged to draw the air from the outer protective air layer 34 through the inlet 36 and return air passage 38 and to cause it to flow rearwardly through a passage 64 to the vertically extending protective air duct 24. An additional blower 66 serves to draw the air from the inner refrigerated layer of air 42 through the inner refrigerated air inlet 44 and cold air return passage 46 and to cause it to flow over the evaporators 12 and 14 to the vertically extending inner refrigerated air duct 22. The inner and outer vertical air ducts are preferably arranged in heat exchanging relation so as to cause the protective layer of air to be cooled by heat exchange through a common divider wall 68. In this way, the protective air layer may be maintained at a temperature lower than that of the ambient air but somewhat higher than that of the air forming the inner refrigerated air layer 42 which circulates adjacent the display space and serves to maintain the display space and the products therein at a desired temperature.

In order to permit defrosting of the evaporator coils 12 and 14, electrical resistance elements 70 are located adjacent the evaporators or elsewhere. Such defrosting means may be energized at suitable intervals, say every 12 or 24 hours, and the defrosting cycle may be continued for a sufiicient period of time to assure the removal of frost or ice from the evaporators and from other surfaces contacted by the circulated refrigerated air during the longer and usual refrigerating cycle of operation of the refrigerating system. Suitable control means such as a time clock or the like 71 may be provided for initiating the defrosting cycle and energizing the heating elements 707 while terminating the flow of refrigerant to the evaporators 12 and 14 and for deenergizin'g the defrosting means and renewing flow of refrigerant to the evaporators during the refrigerating cycle of operation.

When the articles to be refrigerated and displayed are dairy products, meats or the like, the temperature to be maintained in the display space in will be above freezingsay about 40 F.and the air circulated through the refrigerated air duct 22 will be somewhat iowersay 30 to F.to overcome heat loss through the walls of the case and temperature losses incident to the operation of the air curtain and its interruption by persons reaching into the case to remove articles therefrom. On the other hand, when the articles to be refrigerated and displayed are frozen foods, ice cream and the like, the temperature maintained in the display space will generally be 0 F. or below and the air circulated through the refrigerated air duct 22 may be at a temperature as low as 20 F.

The temperature of the air circulated through the refrigerated air duct during the refrigerating cycle of operation will, in each case, be determined by the size, type, and number of the evaporator coils 12 and 14 provided, the adjustment of expansion valves, and the refrigerating capacity or adjustment of the various elements of the refrigerating means employed.

In contrast, the temperature of the air circulated through the refrigerated air duct 22 and over the evaporators 12 and i4 and other surfaces from which frost and ice are to be removed during the defrosting cycle will be approximately the same in all cases in that it wiil be substantially above freezingsay about to F.

in order to prevent the inner surface of the rear metal panel 23 of the display space from attaining similar relatively high temperature, or temperatures sufficiently high to melt or soften articles in contact therewith or adjacent thereto, the panel 269 is provided with an inner layer of thermal insulating material 72. The thermal insulation 72 preferabiy is of limited thickness and need only be sufiiciently effective to reduce the rate of heat transfer from the refrigerated air duct 22 to the panel 21 so as to prevent the panel 2@ from attaining a temperature above freezing or sufficiently high to adversely affect the products adjacent thereto during the relatively short period of time required for defrosting the evaporators or other surfaces from which ice and frost are to be removed.

As shown in FIG. 1, the insulation 72 extends throughout the area of the rear panel 28 of the display space and the refrigerated air duct 22 is devoid of air discharge openings so that none of the heated air circulated there through during the defrosting cycle is discharged into the display space. Therefore, the temperature of the air in the display space is not raised appreciably and there is substantially no loss of refrigeration by reason thereof. Moreover, during the relatively prolonged refrigerating cycle of operation, the rear panel 243 will attain and remain at the desired temperature which will be about 46 F. when dairy products are being displayed and will be well below freezing when ice cream or frozen foods are being displayed. Further, in order to maintain a desired temperature differential between the inner layer of air 42 and the protective layer of air 34 which form the air curtain 48, the common divider wall 63 between the refrigerated air duct 22; and the protective air duct 2% may be provided with a layer of limited insulation material 74 for reducing the rate of heat transfer from one duct to the other.

The construction thus provided, when used to preserve and display dairy products and the like, renders it possible to maintain the display space at a desired temperature above freezing. At the same time, it is possible to prevent those surfaces which are in heat exchanging relation with the refrigerated air duct 22 and exposed to the interior of the display space from attaining such a low temperature during the refrigerating cycle as to cause undesired sweating or possible freezing of articles in contact with such surfaces.

When the display case is operated at low temperatures to maintain the display space weil below freezing for preservation and display of frozen foods, the rear panel will be reduced to the desired low temperature by heat exchange with the low temperature air circulated through the refrigerated air duct 22. Although the thermal insulation 72 is interposed between the panel 20 and the cold air in the refrigerated air duct, the insulation then serves in effect as a limited refrigeration storage or heat transfer delaying means, which will delay, but not prevent, the panel 20 from reaching the desired low temperature during the relatively prolonged refrigerating cycle of operation.

During the defrosting period, when the air circulated through the refrigerated air duct 22 is raised to a temperature of or F., the delayed heat transfer through the insulation 72 and panel 20, serves to prevent any rapid rise in temperature of the panel 20 so that it seldom if ever reaches a temperature above freezing during the relatively short time required for the defrosting cycle. As a result, the tendency for articles in contact with the rear panel 20 or adjacent thereto to melt and any tendency for water to accumulate on and about the articles is eliminated. Accordingly, the subsequent formation of ice which would cause packages to freeze together and stick to the panel or shelf when refrigeration is renewed is overcome. The articles are instead kept in a frozen condition at all times without deterioration and can be readily removed from the display space at all times.

The shelves 56, 58 and 60 on which articles are supported within the display space are preferably mounted on vertically extending and horizontally spaced mullions 7 8 located adjacent the rear panel 20 of the display space. As shown in FIGS. 2 and 3, the mullions 78 may be supported by brackets 80 secured to the metal divider 68 which separates the refrigerated air duct 22 from the protective air duct 24. Connecting members 82 are interposed between the brackets 80 and the mullions 78 and are formed with inwardly and laterally turned edges as shown at $4 and 86 respectively to aid in supporting and positioning the marginal inturned edges 88 of the metal sheets 90 which cooperate to form the panel 20 at the rear of the display space. The mullions 78 are secured to the brackets 80 by bolts 92 or the like which pass through the central supporting portion 94 of the connecting members 82. The brackets 80 may be provided at vertically spaced points in the rear of the case as required to provide adequate support for the shelves 56, 58 and 60.

Any suitable number of shelves may be employed and they may be adjustably mounted on the mullions 76 at whatever elevations or in whatever vertically spaced relation may be desired. For this purpose, the mullions 78 are provided with a plurality of vertically extending slots or openings 96 whereas the shelves may be provided with rearwardly and upwardly extending lugs or other retaining means 98 adapted to be inserted through the openings 96 to support the shelves in any desired positions within the display space 16.

In the alternative form of the invention illustrated in FIG. 4 of the drawings, the display case has an insulated base 100, an insulated rear wall 102, an insulated top 104, and an insulated lower front wall 106 spaced from the top 104 to provide an access opening 108. The display space 110 of the display case has a bottom panel 112, a lower rear panel 114, an upper rear panel 116 and a top panel 118.

The air curtain 120 which protects the display space against the entry of ambient air embodies an inner refrigerated layer of air 122 directed across the access opening from a downwardly directed outlet 124, and a protective layer of air 126 directed downwardly from an outlet 12% located adjacent the outlet 124. The two layers of air forming the air curtain are received by a common air return inlet 130 located adjacent the upper portion of the lower insulated front wall 106 of the case so as to pass through the passage 132 to a plenum chamber 134 beneath the bottom panel 112 of the display space.

A dehydrating coil or evaporator 136 is located in the plenum chamber 134 and a blower 138 is also located in the plenum chamber for forcing the return air received from the passage 132 through both a refrigerated air duct 140 and a protective air duct 142. Refrigerating elements such as the evaporators 144, 146 and 148 are located in the refrigerated air duct 140 whereas the protective air duct 142 need not contain any refrigerating means but may be unobstructed while being located in heat exchanging relation with the refrigerated air duct through a metal divider 150. The amount of air passing through the refrigerated and protective air ducts from the plenum chamber 134 will thus be proportioned and vary in response to the build up of frost and ice on the evaporators 144, 1 16 and 148 and the restriction or back pressure presented to the flow of air through the refrigerated air duct 140 as disclosed in copending application Ser. No. 477,681. If desired, the metal divider 150 may be provided with a layer of thermal insulation 151 to assure the desired temperature differential between the protective air layer 126 and the inner air layer 122 of the air curtain 120.

The air forming the protective layer of air 126 of the air curtain flows from the plenum chamber 134 through the horizontal or inlet passage 152 to the vertically extending protective air duct 142 and thence forward through passage 154 beneath the insulated top 104 of the case to the front air discharge outlet 123. The protective air is at the same time cooled to some extent by heat exchange through the metal divider 150 and insulation 151 so as to attain a temperature :below that of the ambient air but higher than that of the refrigerated layer of air 12.2 of the air curtain 120.

The air which forms the refrigerated layer of air 122 flows from the plenum chamber 134 through passage 1'56 and over evaporator 144 to the vertical refrigerated air duct 1%. In passing upward through the air duct 14%, the air first passes over the evaporator 146 and a portion thereof flows forward and outward through a hollow shelf 158 so as to be discharged through an outlet 160 toward the common return air inlet 130 adjacent the lower front wall 166 of the case. At the same time, a further portion of the air flowing upward through the refrigerated air duct 140 passes upward over the evaporator 14-3 and thence forward through passage 152, above the top panel 118 of the display space to the inner air discharge outlet 124- to form the inner refrigerated layer of air 122 of the air curtain 120.

In accordance with the present invention, the refrigerated air duct 140 is provided with a layer of insulating material 164 of limited thickness which is located on the rear surface of the lower rear panel 114 of the display space and between the panel 114 and the evaporator 146. In a similar way, a layer of insulating material 166 is located on the rear face of the upper rear panel 116 of the display space between panel 116 and evaporator 148. In order to prevent or limit the transfer of heat upwardly through the article supporting surface 168 of the hollow shelf 15-3 during the defrosting cycle, the surface 168 is provided with a thermal barrier such as a layer of insulating material 170 applied to the lower face of the surface 168. Thermal insulation may also be applied at 171 beneath the shelf 158 if desired and thermal insulation 172 may be located above the top panel 113 of the display space.

Heating elements for use in defrosting the various coils or evaporators employed in the display case are located at suitable points as indicated, for example, at 174 to raise the temperature of the air passing over the coils during the defrosting cycle of operation of the case. With this construction, and as described in connection with that form of the invention illustrated in FIG. 1, the layers of insulating material 154 and 166 on the rear faces of the panels at the rear of the display space and the thermal barrier 170 adjacent the articles on the shelves or adjacent said panels, serve to protect the rear panels 114 and 116 and the supporting surface 163 of the shelf against rapid and undue rise in temperature during the defrosting cycle when relatively warm air is passed over the evaporators and the surfaces of the refrigerated air duct adjacent the rear panels of the display space and through the hollow shelf 153. In this way, the articles on display are protected against an undesired rise in temperature when the case is being defrosted so that accumulations of water and softening or damage to the products on display is reduced to a minimum or eliminated altogether. Accordingly, when the refrigerating cycle is resumed, there will be no ice formation to cause the packages or articles to be frozen together or to stick to the shelves or surfaces engaged thereby and repeated softening and refreezing of products with attendant deterioration thereof will not occur.

The principal and actual operation of display cases embodying the present invention differs fundamentally from the prior art in that the insulation located between the refrigerated air duct and the panels exposed to the interior of the display space functions as a heat transfer delaying and temperature holding means which serves to prevent or minimize temperature fluctuations of such exposed surfaces which otherwise tend to cause sweating of said surfaces when the case is operated at temperatures above freezing or melting of frozen products at a temperature below freezing so that the original high quality of the products is preserved without danger of deterioration.

While the forms of the self service display cases shown in the drawings and described above are typical of those which may be employed in the practice of the present invention, it will be apparent that the form, construction and arrangement of the various elements of the combination are capable of numerous changes and modifications as desired. In view thereof, it should be understood that the particular embodiments of the invention disclosed are intended to be illustrative only and are not intended to limit the scope of the invention.

I claim:

1. In a refrigerated display case of the type which has a display space therein with an access opening in the front of the case and means for maintaining products within said display space at desired temperature and for establishing an air curtain across said access opening, including an air inlet located adjacent one side of said access opening, means for circulating at least a portion of the air from said air curtain through said inlet and about the display space through a refrigerated air duct in heat exchanging relation with a surface exposed to the interior of said display space to an air outlet located adjacent the opposite side of said access opening, and a refrigerant evaporator over which air from said air curtain is circulated and by which said air is reduced to a temperature below said desired temperature prior to its passage through said duct to said outlet; the combination of heating means periodical- 1y operable during a defrosting cycle to raise air passed over the evaporator and through said refrigerated air duct to a temperature above freezing, and means for preventing said exposed surface of said display space from rising to said temperature above freezing during said defrosting cycle comprising thermal insulation located between said exposed surface and said refrigerated air duct.

2. The combination as defined in claim 1 wherein said exposed surface of the display space embodies rear panels and a top panel which extend throughout substantially the entire area of said display space at the rear and top thereof, and said thermal insulation extends throughout substantially the entire area of said panels.

3. The combination as defined in claim 1 wherein said desired temperature is below freezing.

4. The combination as defined in claim 1 wherein at least one shelf is located in said display space and has a rear edge located adajcent said exposed surface of the display space and a front edge spaced inwardly from a line extending from said air outlet to said air inlet.

5. The combination as defined in claim 1 wherein said refrigerated air duct is in the form of a continuous passage extending from said air inlet to said air outlet and is closed about the sides thereof throughout the length there of.

6. The combination as defined in claim 1 wherein a protective air duct is located in heat exchanging relation with said refrigerated air duct and has an air outlet located adjacent and in front of said air outlet of the refrigerated air duct, and means for circulating air from said air curtain through said protective air duct to said outlet.

7. The combination as defined in claim I; wherein thermal insulation is located between said refrigerated air duct and said protective air duct.

8. The combination as defined in claim 6 wherein said protective air duct has an air inlet located adjacent and in front of the air inlet for said refrigerated air duct, and independent means are provided for circulating air from said air curtain through the protective air duct from the inlet to the outlet thereof.

9*. The combination as defined in claim 4 wherein ver- 'cally extending mullions are located at the rear of said display space and a plurality of shelves are adjustably mounted on said mullions in vertically spaced relation.

10. The combination as defined in claim 9 wherein the exposed surface of said display space at the rear thereof embodies panels which extend between said mullions, and said panels and thermal insulation are supported by said mullions.

11. The combination as defined in claim 4 wherein said shelf is hollow and presents an upper article supporting surface with thermal insulating means extending throughout substantially the entire area thereof, the rear of said shelf having an opening therein communicating with said refrigerated air duct and the shelf having an air outlet located near the front thereof.

12. The combination as defined in claim 11 wherein the rear of said display space above and below said hollow shelf embodies panels having thermal insulation located between said panels and said refrigerated air duct.

References Cited UNITED STATES PATENTS 2,822,672 2/1958 Dickson 62-256 2,836,039 5/1958 Weber 62256 3,182,467 5/1965 Beckwith 62256 3,304,740 2/1967 Dickson 62256 WILLIAM J. WYE, Primary Examiner. 

1. IN A REFRIGERATED DISPLAY CASE OF THE TYPE WHICH HAS A DISPLAY SPACE THEREIN WITH AN ACCESS OPENING IN THE FRONT OF THE CASE AND MEANS FOR MAINTAINING PRODUCTS WITHIN SAID DISPLAY SPACE AT DESIRED TEMPERATURE AND FOR ESTABLISHING AN AIR CURTAIN ACROSS SAID ACCESS OPENING, INCLUDING AN AIR INLET LOCATED ADJACENT ONE SIDE OF SAID ACCESS OPENING, MEANS FOR CIRCULATING AT LEAST A PORTION OF THE AIR FROM SAID AIR CURTAIN THROUGH SAID INLET AND ABOUT THE DISPLAY SPACE THROUGH A REFRIGERATED AIR DUCT IN HEAT EXCHANGING RELATION WITH A SURFACE EXPOSED TO THE INTERIOR OF SAID DISPLAY SPACE TO AN AIR OUTLET LOCATED ADJACENT THE OPPOSITE SIDE OF SAID ACCESS OPENING, AND A REFRIGERANT EVAPORATOR 